Clean Energy

Like solar and wind, nuclear energy produces next to no CO₂ emissions when compared to fossil fuels like coal and gas. But unlike solar and wind, nuclear power can constantly provide electricity when it is needed<a href='https://energy.mit.edu/wp-content/uploads/2018/09/The-Future-of-Nuclear-Energy-in-a-Carbon-Constrained-World.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a> (that means even at nighttime when the wind isn't blowing!).

Nuclear energy is a form of energy that is stored in the core of atoms<a href='https://www.iaea.org/newscenter/news/what-is-nuclear-energy-the-science-of-nuclear-power' target='_blank'><img src='/img/courses/ref.svg'/></a>. Harnessing this energy currently provides about 10% of the world's electricity, but it has seen some opposition due to a few highly visible accidents<a href='https://www.iaea.org/newscenter/news/what-is-nuclear-energy-the-science-of-nuclear-power' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.iea.org/reports/nuclear-power-in-a-clean-energy-system' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.sciencedirect.com/science/article/abs/pii/S1350448713000267' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.sciencedirect.com/science/article/abs/pii/S1350448712001680' target='_blank'><img src='/img/courses/ref.svg'/></a>. On the other hand, when facing a challenge as bad as climate change, it’s worth carefully weighing up our options. To do this, let's start by understanding how nuclear power works.

How do we get energy from splitting atoms?

Atoms are made up of protons, neutrons, and electrons<a href='https://www.britannica.com/science/atom' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.energy.gov/science/doe-explainsnuclei#:~:text=Atomic%20nuclei%20consist%20of%20electrically,the%20mass%20of%20the%20atom' target='_blank'><img src='/img/courses/ref.svg'/></a>. Protons and neutrons are clustered together in the centre of the atom forming the nucleus<a href='https://www.britannica.com/science/atom' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.energy.gov/science/doe-explainsnuclei#:~:text=Atomic%20nuclei%20consist%20of%20electrically,the%20mass%20of%20the%20atom' target='_blank'><img src='/img/courses/ref.svg'/></a>.

Each element in the periodic table is defined by the number of protons it has<a href='https://ptable.com/?lang=en#Properties' target='_blank'><img src='/img/courses/ref.svg'/></a>. But atoms of the same element with the same number of protons can have different numbers of neutrons - these atoms are called isotopes<a href='https://www.energy.gov/science/doe-explainsisotopes' target='_blank'><img src='/img/courses/ref.svg'/></a>.

Nuclear power is based on nuclear fission, where some isotopes split into two smaller nuclei when you fire a neutron at them<a href='https://nrl.mit.edu/reactor/fission-process' target='_blank'><img src='/img/courses/ref.svg'/></a>.

Most nuclear reactors use Uranium-235 (U-235), an isotope of Uranium that has 92 protons and 143 neutrons<a href='https://nrl.mit.edu/reactor/fission-process' target='_blank'><img src='/img/courses/ref.svg'/></a>. The isotope is named Uranium-235 because the sum of the number of its protons and neutrons is 235. U-235 is somewhat unstable and can split - especially if acted on by an outside source like a free neutron<a href='https://nrl.mit.edu/reactor/fission-process' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.britannica.com/science/spontaneous-fission' target='_blank'><img src='/img/courses/ref.svg'/></a>!

When a neutron is fired at U-235, the atom splits and you get<a href='https://nrl.mit.edu/reactor/fission-process' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://nrl.mit.edu/reactor/fission-process' target='_blank'><img src='/img/courses/ref.svg'/></a>:

What's the difference between a nuclear bomb and a nuclear power plant?

Do you notice anything? One neutron causes a U-235 atom to split, releasing energy and more neutrons<a href='https://www.nrc.gov/reading-rm/basic-ref/students/for-educators/02.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://nrl.mit.edu/reactor/fission-process' target='_blank'><img src='/img/courses/ref.svg'/></a>. These new neutrons can cause more U-235 to split, and the process keeps repeating<a href='https://nrl.mit.edu/reactor/fission-process' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.nrc.gov/reading-rm/basic-ref/students/for-educators/02.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a>. So, if you pack a lot of U-235 atoms into one place, you get a...nuclear chain reaction<a href='https://www.eia.gov/energyexplained/nuclear/' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://nrl.mit.edu/reactor/fission-process' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.nrc.gov/reading-rm/basic-ref/students/for-educators/02.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a>!

The chain reaction would grow exponentially, releasing a lot of energy very quickly.

The chain reaction would cause the U-235 fuel to be used up too quickly, meaning the nuclear plant wouldn’t run for long enough, but it isn’t dangerous.

If each split causes two or more splits, all the power will be released very quickly<a href='https://www.britannica.com/science/actinoid-element/Physiological-properties-of-the-actinoids#ref622136' target='_blank'><img src='/img/courses/ref.svg'/></a>. This is what happens in a nuclear bomb<a href='https://www.britannica.com/science/actinoid-element/Physiological-properties-of-the-actinoids#ref622136' target='_blank'><img src='/img/courses/ref.svg'/></a>. In nuclear power reactors, we want each split to cause exactly one more split<a href='https://nrl.mit.edu/reactor/fission-process' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.nrc.gov/reading-rm/basic-ref/students/for-educators/02.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a>. This keeps the reaction stable and constant<a href='https://www.nrc.gov/reading-rm/basic-ref/students/for-educators/02.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://nrl.mit.edu/reactor/fission-process' target='_blank'><img src='/img/courses/ref.svg'/></a>.

Move the fuel in and out of the reactor core

Absorb some of the neutrons such that 1 neutron produced per split goes on to cause only 1 more split

The number of neutrons that are able to go on and cause a split must be continuously regulated in order to control the chain reaction<a href='https://spark.iop.org/collections/nuclear-fission' target='_blank'><img src='/img/courses/ref.svg'/></a>. This is done by moving control rods made of substances that absorb neutrons, in and out of the reactor core<a href='https://spark.iop.org/collections/nuclear-fission' target='_blank'><img src='/img/courses/ref.svg'/></a>.

At the same time, to maintain a stable chain reaction we need to be able to rely on the likelihood that a neutron will collide with a U-235 nucleus<a href='https://spark.iop.org/collections/nuclear-fission' target='_blank'><img src='/img/courses/ref.svg'/></a>. There are two ways that this is done: enrichment and moderation<a href='https://spark.iop.org/collections/nuclear-fission' target='_blank'><img src='/img/courses/ref.svg'/></a>.

So together, the moderator and the control rods stabilise and control the reaction from the enriched fuel rods<a href='https://www.bbc.co.uk/bitesize/guides/zxwkjty/revision/3' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://spark.iop.org/collections/nuclear-fission' target='_blank'><img src='/img/courses/ref.svg'/></a>.

Remember that each time a U-235 atom splits, heat is released? Nuclear reactors use this heat to create steam<a href='https://www.britannica.com/technology/nuclear-power' target='_blank'><img src='/img/courses/ref.svg'/></a>. This steam then makes turbines spin which powers a generator - just like in a fossil fuel power station<a href='https://www.britannica.com/technology/nuclear-power' target='_blank'><img src='/img/courses/ref.svg'/></a>!

The most common type of nuclear reactor is the Pressurised Water Reactors (PWR)<a href='https://www.nrc.gov/reactors/pwrs.html' target='_blank'><img src='/img/courses/ref.svg'/></a> which contains two water loops<a href='https://www.nrc.gov/reading-rm/basic-ref/students/for-educators/04.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.britannica.com/technology/nuclear-power' target='_blank'><img src='/img/courses/ref.svg'/></a>. The first, called the primary circuit, absorbs the heat from the fission of U-235<a href='https://www.nrc.gov/reading-rm/basic-ref/students/for-educators/04.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a>.

This hot water then runs through a pipe that goes through a separate loop of water<a href='https://www.nrc.gov/reading-rm/basic-ref/students/for-educators/04.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a>.

The steam created from boiling this second loop of water is then used to spin a turbine<a href='https://www.nrc.gov/reactors/pwrs.html' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.nrc.gov/reading-rm/basic-ref/students/for-educators/04.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a>. This last part of the process is just like a coal plant.

We end up with radioactive waste that we don't know what to do with

When cooling mechanisms fail due to a power outage, the reactor can heat up a lot and, due to high water vapour pressures, explode.

Both of the above are problems, so let’s break them down.

Nuclear causes far fewer deaths than coal

In fact, nuclear accidents are extremely unlikely and altogether cause far fewer deaths than fossil fuels (mainly because burning fossil fuels releases deadly air pollution)<a href='https://www.sciencedirect.com/science/article/abs/pii/S0959652615009877?via%3Dihub' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(07)61253-7/fulltext' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://doi.org/10.1021/es3051197 ' target='_blank'><img src='/img/courses/ref.svg'/></a>.

A big downside to nuclear fission is the radioactive waste<a href='https://www.jstor.org/stable/24106030?casa_token=bDMaPLu2fu8AAAAA%3ACG85qKUTkT5HSboL1V6EWjoGRZsObJWYJpBc99Tm4-Dg7fZLhR5GC_K_2p__ppGD8NGBX_A5KZIErEXvSuyrffJeSihRFxxVIHcq_MV8hmQyOEyoJndB&seq=1#metadata_info_tab_contents' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://onlinelibrary.wiley.com/doi/full/10.1002/wer.1442?casa_token=F2B2i07YUqgAAAAA%3ABd8SR6zbFkTyDC4koXvVNnP0-1gJPK_a6nHcHoegizOCnJStXXI9CAvxHpf7n7-xsxi9HO03bnv15qSD' target='_blank'><img src='/img/courses/ref.svg'/></a>. This waste is put into three categories:<a href='https://www.iaea.org/publications/14739/status-and-trends-in-spent-fuel-and-radioactive-waste-management' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.iaea.org/sites/default/files/18/10/radioactivewaste.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a>

High-level nuclear waste, although only accounting for less than 1% of all waste, presents a significant problem for long-term storage<a href='https://www.iaea.org/publications/14739/status-and-trends-in-spent-fuel-and-radioactive-waste-management' target='_blank'><img src='/img/courses/ref.svg'/></a>.

One solution is to create deep geological repositories, where spent nuclear fuel can be securely stored for thousands of years<a href='https://link.springer.com/article/10.1007/s12205-011-0012-8' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.iaea.org/publications/14739/status-and-trends-in-spent-fuel-and-radioactive-waste-management' target='_blank'><img src='/img/courses/ref.svg'/></a>. Some countries are leading the way in this field, with Finland being the first to construct such a site, over 100 metres deep, with careful consideration given to its long-term stability<a href='https://link.springer.com/article/10.1007/s12205-011-0012-8' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.iaea.org/newscenter/news/finlands-spent-fuel-repository-a-game-changer-for-the-nuclear-industry-director-general-grossi-says' target='_blank'><img src='/img/courses/ref.svg'/></a>.

Aside from the perception of the safety of nuclear power and the problem of dealing with nuclear waste, an undeniable problem is that building new nuclear plants takes a long time and is expensive<a href='https://energy.mit.edu/wp-content/uploads/2018/09/The-Future-of-Nuclear-Energy-in-a-Carbon-Constrained-World.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a>.

Construction time is, on average, over 5 years and while other clean energy sources have become cheaper and cheaper, the cost of setting up a nuclear power station has remained high<a href='https://energy.mit.edu/wp-content/uploads/2018/09/The-Future-of-Nuclear-Energy-in-a-Carbon-Constrained-World.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.statista.com/statistics/712841/median-construction-time-for-reactors-since-1981/' target='_blank'><img src='/img/courses/ref.svg'/></a>. In fact, it is not considered profitable to build new reactors in Western countries today<a href='https://energy.mit.edu/wp-content/uploads/2018/09/The-Future-of-Nuclear-Energy-in-a-Carbon-Constrained-World.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a>.

Nuclear is a near zero-carbon and reliable energy source<a href='https://www.eia.gov/energyexplained/nuclear/' target='_blank'><img src='/img/courses/ref.svg'/></a>.

But today’s nuclear power has a waste problem<a href='https://www.jstor.org/stable/24106030?casa_token=bDMaPLu2fu8AAAAA%3ACG85qKUTkT5HSboL1V6EWjoGRZsObJWYJpBc99Tm4-Dg7fZLhR5GC_K_2p__ppGD8NGBX_A5KZIErEXvSuyrffJeSihRFxxVIHcq_MV8hmQyOEyoJndB&seq=1#metadata_info_tab_contents' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://onlinelibrary.wiley.com/doi/full/10.1002/wer.1442?casa_token=F2B2i07YUqgAAAAA%3ABd8SR6zbFkTyDC4koXvVNnP0-1gJPK_a6nHcHoegizOCnJStXXI9CAvxHpf7n7-xsxi9HO03bnv15qSD' target='_blank'><img src='/img/courses/ref.svg'/></a>, and the construction time and cost of setting up a nuclear power station are so great that it is not considered profitable in many countries<a href='https://energy.mit.edu/wp-content/uploads/2018/09/The-Future-of-Nuclear-Energy-in-a-Carbon-Constrained-World.pdf' target='_blank'><img src='/img/courses/ref.svg'/></a>.

On the other hand, meltdowns are so rare and cause comparably few deaths that nuclear power is, per unit energy, one of the safest forms of energy available<a href='https://www.sciencedirect.com/science/article/abs/pii/S0959652615009877?via%3Dihub' target='_blank'><img src='/img/courses/ref.svg'/></a><a href='https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(07)61253-7/fulltext' target='_blank'><img src='/img/courses/ref.svg'/></a>!

In the next chapter, we will look at new ideas in nuclear energy that could help solve the problems today’s nuclear has.

NucIncrease

2019EnergyEmissions

AtomNuc

FormsOfEnergy

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Pressurised1

ChilliU235

BaseloadOk

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study

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Nuclear Power

Nuclear Power: Should We be Using It?

Number One Climate Problem

Solar & Wind

Energy Storage

Fossil Fuels

Solar Power

Wind Power

Hydropower

100% Renewables

Generation III+ Nuclear

Geothermal Energy

Nuclear Fusion

Can we make Fusion work?

Everything Electric

Hydrogen

Open Problems

Dr. Chiam Sing Ying

Dr. Gareth Griffiths

Kaan Bolat

Clean Energy (Renewables & Nuclear) is the most important part of the solution. How can we power the world sustainably?